1. Field of the Invention
The present invention is broadly concerned with expandable sealant and baffle compositions for sealing hollow structural members of vehicles, and methods for making and using such compositions. The compositions are prepared by forming an expandable mixture including a first thermoplastic resin (preferably an SBS block co-polymer) and an epoxy resin (preferably a bisphenol A-based liquid epoxy resin). The compositions preferably also include a second thermoplastic resin (preferably a polystyrene) different from the first thermoplastic resin, and a compound selected from the group consisting of pigments, blowing agents, catalysts, curing agents, reinforcers, and mixtures thereof. The preferred reinforcers are hydrated amorphous silica and glass microspheres. The compositions of the invention are injection moldable and can be formed into freestanding, self-sustaining parts. Alternately, the compositions of the invention can be supported on lattice-type nylon supports. Upon heating of the compositions to temperatures of at least about 300° F., the compositions greatly expand to form lightweight products having high compressive strengths.
2. Description of the Prior Art
During the fabrication of automobiles, trucks, and similar over-the-road vehicles, many body components present structural members having cavities that require sealing to prevent the entrance of moisture and contaminants which can cause corrosion of the body parts. It is also desirable to greatly strengthen the members while maintaining their light weight. It is also necessary to stabilize these members in order to attenuate noise that would otherwise be transmitted along the length or passage of the cavity. Many of these cavities are irregular in shape or narrow in size, thus making them difficult to properly seal and baffle.
Many attempts have been made to seal these cavities, spraying sealants into the cavity, introducing foam products into the cavity, and using of fiberglass matting and the like. These methods each have their drawbacks. For example, foaming in place presents a problem in that it is difficult to control where the foam travels upon its introduction into the cavity. Furthermore, it is often necessary to introduce an excess amount of foam into the cavity in order to ensure that the cavity is sufficiently sealed. Finally, foams will generally not adhere to the interior surfaces of the cavity walls if those surfaces contain even a small amount of oil.
Self-sustaining foam products, either with or without a non-foam support structure, have been introduced into structural member cavities in an attempt to seal the cavities. However, these methods generally result in the addition of excess weight to the structural member which is undesirable in most instances. Attempts have been made to utilize foam products which are lighter in weight or which do not use a support structure. However, these attempts have generally resulted in products which lack the increased compressive strength necessary to adequately reinforce the structural member.
U.S. Pat. No. 5,755,486 to Wycech is directed towards a structural reinforcement member which includes a thermally expandable resin-based material. The structural member is heated so as to expand the resin-based material, thus locking the reinforcement member in place. However, the compositions disclosed in the '486 patent do not possess sufficient expansion capabilities. As a result, more of the composition is required to adequately fill and seal a particular cavity, thus resulting in added weight to the car and added expense to the automotive manufacturer. Furthermore, the composition disclosed in the '486 patent makes use of fumed silica which leads to a product having a high viscosity and therefore unsuitable for injection molding of the composition.
U.S. Pat. Nos. 5,373,027 and 5,266,133 to Hanley et al. are respectively directed towards expansible sealant and baffle components for sealing and providing an acoustic baffle for cavities in vehicle bodies and methods of making such components. The components expand upon heating, thus sealing the cavity in which they are placed. The components are formed of a composition which includes an ethylene-α,β ethylenically unsaturated carboxylic acid copolymer, a blowing agent, a tackifier, and optionally an additive polymer and a cross-linking agent. While the compositions of the '027 and '133 patents possess sufficient expansion capabilities, they are not strong enough to make suitable reinforcement members.
U.S. Pat. No. 5,506,025 to Otto et al. is concerned with an expandable baffle apparatus for sealing an automobile cavity. The apparatus of the '025 patent includes a piece of heat expandable sealing material formed in a shape corresponding to the shape of the cross-section of the cavity to be sealed. The sealing material is supported by an open lattice support element formed of material such as nylon. While the apparatus of the '025 patent is suitable as a cavity sealant and baffle apparatus, it does not provide sufficient reinforcement to the structural member forming the cavity in which the apparatus is placed.
There is a need for an injection moldable, expandable, lightweight composition which acts as both a sealant to prevent the entrance of undesirable components into vehicle cavities and a baffle to diminish or prevent noises which normally travel along the length of the cavity. Furthermore, this composition should have a high compressive strength so that it reinforces the structural members in which it is used.